Bench Testing: Diode

WARNING: This page is about a different car, the 2004 Subaru Forester and 2003 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.

CAUTION: Never use a mega tester (measuring use for high voltage) or any other similar measure for this test; otherwise, the diodes may be damaged.

Check for continuity between the diode lead and positive side heat sink. See Fig 1 . The positive diode is in good condition if resistance is 1 ohms or less only in the direction from the diode lead to heat sink.
Check for continuity between the negative side heat sink and diode lead. See Fig 2 . The negative diode is in good condition if resistance is 1 ohms or less only in the direction from the heat sink to diode lead.

Fig 1: Checking Positive Diode

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Fig 2: Checking Negative Diode

Courtesy of SUBARU OF AMERICA, INC.